A promising method for improving light-absorption in thin-film devices is demonstrated via electrode structuring using Anodic Alumina Oxide (AAO) templates. We present nano-scale concave Al structures of controlled dimensions, formed after anodic oxidation of evaporated high purity aluminum (Al) films and alumina etching. We investigate both experimentally and theoretically the field-enhancement supported by these concave nanostructures as a function of their dimensions. For the experimental investigations, a thin layer of organic polymer coating allows the application of a nondestructive laser ablation technique that reveals field-enhancement at the ridges of the Al nanostructures. The experimental results are complemented by finite-difference time-domain (FDTD) simulations, to support and explain the outcome of the laser ablation experiments. Our method is easily up-scalable and lithography-free and allows one to generate nanostructured electrodes that potentially support field-enhancement in organic thin-film devices, e.g., for the use in future energy harvesting applications.